The angle at which you hold your ankle while pedaling is a largely matter of preference. All else equal, if you tend to pedal toe down the saddle will be lower than if you pedal toe level or toe up. The difference can be as much as several cm. Ride for a while, on the road or a trainer so that your ankle assumes it's normal angle and then assess the degree of knee bend at the bottom of the stroke. ~20 degrees is the usual.